Bumper bars for vehicles are often mounted on crash boxes that are mounted at the ends of the side rails of the vehicle. EP 1 477 371 A2 shows a crash box of the type described above. This has grooves or dents on all of its four plane sides and holes at all of its four corner edges at the centre of the grooves, and these holes act as deformation initiators. An even loading curve is obtained, but the holes reduce the level of load since the corners have the greatest significance for the loading level.